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PROTECTION OF GRAPEVINE FROM POWDERY MILDEW BY USING NATURAL SUBSTANCES AND
THE MICROBIAL ANTAGONIST AMPELOMYCES QUISQUALIS
Agostino Santomauro (1) , Giuseppe Tauro (2) , Maurizio Sorrenti, Francesco Faretra (1)
(1) Dipartimento Protezione delle Piante e Microbiologia Applicata, University of Bari
(2) Centro di Ricerca e Sperimentazione in Agricoltura "Basile Caramia", Locorotondo (Bari)
Powdery mildew, caused by Uncinula necator (Schw.) Burr., is one of the most common and severe diseases of
grapevine, causing heavy yield losses wherever the crop is intensively grown. Many fungicides are available for its
control. Recently, however, the rapid diffusion of organic agriculture has stressed out the lack of solid experimental
data on the effectiveness of natural substances and microbial antagonists that are potential alternatives to the use of
chemicals.
The present paper reports the results of field trials carried out in 1998, 2000 and 2001 in order to evaluate the
effectiveness of natural substances and the mycoparasite Ampelomyces quisqualis Ces. for the control of grapevine
powdery mildew.
The statistical scheme of randomized blocks with four replications and plots of 8-10 plants was adopted in all
trials. The first two sprays were always carried out at the beginning and at the end of blossoming. Afterwards,
treatments were carried out at one-week intervals until véraison. The tested spray schedules are listed below.
Tested compounds Formulates Rates Year of employment
(g or ml/ha) 1998 2000 2001
Ampelomyces quisqualis +
AQ 10 (Bio Intrachem)
50 + • • •
Mineral oil
Ultra Fine Oil (Bio Intrachem) 2000
Ampelomyces quisqualis +
AQ 10 (Bio Intrachem)
50 +
•
Pinolene
Vapor-Gard (Bio Intrachem) 2000
Sodium bicarbonate +
RPH (Carlo Erba)
5000 + • • •
Mineral oil
Ultra Fine Oil (Bio Intrachem) 2000
Sodium bicarbonate +
RPH (Carlo Erba)
5000 +
•
Pinolene
Vapor-Gard (Bio Intrachem) 2000
Sodium bicarbonate RPH (Carlo Erba) 5000 •
Foliar fertilizer Trym (Italpollina) 150 •
Powder milk Vigor Latte (Mignini) 10000 •
Mineral oil Ultra Fine Oil (Bio Intrachem) 10000 •
Pinolene Nu - Film 17 (Chimiberg) 10000 •
Pinolene Vapor-Gard (Bio Intrachem) 10000 • •
Potassium salts of fatty acids MYX 403.2-050 (Mycogen) 10000 •
Sulphur Zolfo WG (Bayer) 2500 •
Sulphur Kumulus Tecno (Syngenta) 5000 •
Symptom severity was assessed two to four times for each trial by observing 250-300 bunches per plot and
counting infected berries. An empirical scale with 8 class of infection was used to calculate the following parameters:
the percentage of infected organs (Tehon’s “prevalence”), the disease severity (Tehon’s “destructiveness”) and its
weighted average value (according to the McKinney Index). All data were submitted to variance analysis and mean
values were separated by Duncan’s Multiple Range Test.
During 1998 and 2000, powdery mildew infections interested 77% and 65% of bunches in untreated plots,
respectively. The values of McKinney Index, however, were not very high, reaching 17% and 13%, respectively. Under
these conditions of medium disease pressure, all of the tested compounds showed to be effective against powdery
mildew, decreasing significantly symptom severity on both berries and rachis, as compared to the untreated check. In
particular, sodium bicarbonate (used either alone or in mixture with mineral oil) and pinolene showed the highest
effectiveness, allowing reductions up to 90% of symptom severity. These results were substantially confirmed even
under the higher disease pressure occurred in the trial carried out in 2001. In that year, powdery mildew symptoms were
observed on 88% of bunches in untreated plots, with a value of McKinney Index as high as 34%. Even under such
conditions, pinolene and sodium bicarbonate, used either alone or in mixture, allowed a significant reduction of the
disease. Moreover, very interesting results were obtained with powder milk that yielded the best control of the disease.
Repeated sprays with pinolene or potassium salts of fatty acids had some negative side effects on bunches, by
removing waxes from the surface of berries and causing persistent bad smell. Repeated sprays with milk left visible
residues, thus getting dirty bunches. Such effects represent a serious limitation for their usage on table grape, but should
be negligible for wine grape.
In conclusion, the tested natural substances and A. quisqualis showed an interesting, although not complete,
effectiveness against grapevine powdery mildew. Yet, their exclusive usage in the protection of table grape seems can
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